Unloading system for compressors



July 1, 1930.

W. E. MATHEWS UNLOADING SYSTEM FOR COMPRESSORS Filed July 2, 1928 5 Sheets-Sheet l Allorney July 1, 1930. w. a MA'rHl-zws 1,769,898

UNLOADING SYSTEM FOR COMPRESSORS Filed July 2, 1928 5 Sheets-Sheet 2 Inventor Attorneys 5 Sheets-Sheet -W. E. MATHEWS UNLOADING SYSTEM FOR coMPREssoRs Filed July 2, 1928 July 1, 1930.

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UNLOADING SYSTEM FOR COMPRESSORS Filed July 2. 1928 s Sheets-Sheet 4 lli KW! WE. Mal/1e ws By wa Attorneys Inventor Patented Julyfl, 1930 rm f; tn

WILLIAM E; MATHEWS, or BIRMINGHAM, ALABAMA, Assrenon TO HARDIE-TYNES MANUFACTURING COMPANY, A'oonron-Arronor ALABAMA UnLoAnrne sYsrEM non ooMrnlnssons A lication filed luly 2, 1928.;K Serial 1%. esasoL-f My invention relates to unloader systems for reciprocating compressors and has for its object the provision of apparatus of thecharacter designated which shall be simple of 5 design and operation and which shall be effective to smoothly and automatically unload. the compressor as it approaches the maXi-.

mum pressure required.

A further ob ect or my invention to pro.-

16 vide unloader apparatus wherein the com pressor is unloaded in aseries'ofgradual steps and the load is taken on 1n a reverse order of gradual steps thereby greatly reducing the shocks to the compressor and its ClIiV-Z ing means, heretofore incident tounloading and loading operations. A still further object to provide 20 sure in opposition to the velocity of medium being, compressed flowing thereby; when.

open, and wherein a predetermined relatively low pressure is employed for opening at;

least some of said valves to provide the early unloading steps, thereby providing more closely graduated steps of unloading than heretofore possible. i Y

A still -further object of invention is to provide a compressor unloading system .3 wherein a master control valve controlsthe H sirable that the degree of unloading'be in accordance with the demandjjfor compressed. medium to avoid shocks which would result? from sudden, total-unloading followed vby the imposition; of full load upon the com;

pressor.

. ferent pressures.

of my invention is unloader" apparatus embodymg. unloader valves operable in response to presas is well known,

developed e the compressor for fatively low pressure Various, means have'hereto fore been proposed to' provide gradual'step unloading for compressors,the most common being the pro,- vision of a plurality of spring biased valves which are opened in response to the pressure developed by the compressor, the springs of said valve being so set that they open at dif' v 7 When open, the pressure passes to pressure'responsive unloader valve and opens them to eflect the unloading of the compressor, Difficulties are encountered in operation with such a system of unloading due to the difficulty-in providing springs for the valves which will operate to provide graduated step unloacling within the narrow limits of pressure and under the conditions of service to which they are subjected.

i Furthermore, the pressure passing the sev-' eral valves,be1ng close'to the maximum pres-.

unloaded one end at a'timethereby entailing different loads on the driving motor atthe opposite ends of the piston'stroke and setting up severe shocks and vibrations in the driv- 111g) motor. Y M l These and other difficultiesare overc'ome by means of my invention and I provide an unloader system wherein the compressor may be evenly unloaded in any desirednumber of graduated steps. These desirable results I are obtained bylpro'viding a master control valve responsive to the pressure developed by the compressor and socon'structed as to bequick opening and quick closing thereby passing a considerable volume of air at'the pressureat which it operates; The unloader valves for the early steps of unloading are operated by pressure from a plurality of auxiliary valves under the'control of the master controlvalve and operable to provide a predetermined relpressure responsive unloadervalves, the pres-. sure.providedbeing suffic ently'low that the unloadervalves are closed by the velocity the medium, being compressed flowing thereby before the compressor piston completes for operation of the the full stroke of the its stroke. By this means the opposite ends of the compressor cylinder may be partially unloaded simultaneously thereby avoiding total unloading of the opposite ends. auxiliary valves are preferably arrangedto operate in series with the master controlwalve. With this arrangement, the oomgessor may be evenly unloaded in any num r of graduated steps. I also provide mw'brmoreauxiliary master control valves arranged in series with the master control valverand which may be arranged in series with. each other to govern the later steps of unloading. By the system outlined I prola Vida dual, even unloading of the compressor,- wholly responsive to the work it is ,ppon to perform and one which I have reliable in operation.

.Apparatus embodying features of my infiovcntipn is illustrated in the accompanying forming a part of this application,

, F1 is aperspective view of a compressor eqmppadwith my improved unloader ap- Fig. 2 is a diagrammatic view illustrative of the operation of the apparatus;

' .FigBis a sectional view of the master conirolwalve;

7 a similar viewof an auxiliary master control valve:

auxiiary control valves which govern the steps of unloading;

Fif. 5 is a sectional elevation ofa pair of l Rig. is an enlarged sectional view of one of the valves shown in Fig. 5, taken along {thelinaVL-VI of Fig. 5; V

Him? is a sectional view of an unloader valvoflmployed with my invention; and

. Fig.3 is a diagrammatic view illustrating I form of my invention. Referring now to the drawings for a-betunderstanding of my invention I show, 1, a compressor comprising a low o cylinder-.10, a high pressure cylinder 11. inter-cooler 12. The low pressure Mr is mounted 'on a pedestal 13 in r lhiehsimprovided an inlet 14 and the high cylinder is mounted on apedestal is connected a discharge conduit l'l 'iirl'rich latter leads to a reservoir 18. The

.comprea'oris driven by any suitable means, I

a motor 19 and preferably'at a tallyconstan't speed. 1 In thefurther of my invention, for the sake of brevityg 'the medium being compressed will be spoken of as air, though it will be obvious thattheWporation will be similar when comany gaseousmedium.

finloader system for the compressor amaster control valve 21, in -com- V municatiomwith the reservoir 18 through a conduit 22 @7116 1a branch conduit 23. A

lehnor zl isprovided between the conduits voir 29 secured to the side of the low pressure cylinder 10. The small reservoir 29' is in heat transfer relation with the water cooling system for the cylinder 10,

the inlet for the water cooling system being shown at 31" and the outlet at 32. This latter feature is provided in order to maintain the low pressure air at an even temperature and insure better operation of the apparatus.

Communicating with the low pressure reservoir 29 is a conduit 33 leading to an auxiliary valve 34 and from thence to a second auxiliary valve 36 formed in a single castin with the valve 34 and communicating. t erewith through a passage 37, see Fig. 5.

Referring now articularly to Fig. 2, I show the front an rear portions of both the high and the low pressure cylinders separately with the.piping and valve arrangement for effecting the gradual unloading of the cylinders when the pressure approaches that at which the compressor is supposed to operate. Suitably mounted near the low pressure cylinder'10 is a housing 41 which houses the master control valve 21, the auxiliary valves 34 and 36 and auxiliary master control valves 42, 43 and 44.

The master control valve 21, which will hereinafter be described in detail, is a spring biased valve responsive to pressure in the reservoir 18 and when open allows air to pass to the valves 34, 42, 43 and 44 through cored passages .46, 47, 48 and 49 respectively. The valves 42, 43, and'44 are also spring biased valves set to operate at a higher pressure than the master control valve 21. When the valve 42 is opened by pressure from the passage 46 it permits pressure to pass through a passage 51 to the auxiliary valve 36.

The auxiliary valve 34 is arranged to open immediately upon opening of the master control valve 21 and. controls the flow of low pressure air, fromthe conduit 33 through a conduit 52 to unloader valves 53 and 54 at the front end of the low pressure cylinder, to unloader valves 56 and 57 at the rear end of the low pressure cylinder 10 and to unloader valves 7 and 60 at. opposite ends, respectively, of

to the auxiliary valve 36,; whereupon low pressure air from the conduit 33 and passage 37 flows through a conduit 61- to an unloader valve 62' atthe front end of the low pressure cylinder and't'o an unloadervalve 63 at the rear end of the low pressure cylinder,'also through aconduit'64 to unloader valves 65 and 7 0 at the front and rear, respectively, of

the high pressure cylinder to provide a second step of unloading.

The auxiliary master control valve 43 is set to open by pressure passing the master control valve 21 and at a higher pressure than that at which the auxiliary master control valve 42 opens, it permits air to pass through a conduit 66. to an unloader valve 67 in the front end ofthe low pressure cylinder and through a conduit 68 to an unloader valve 69 in the front end of the high pressure cylinder.

\ The valves 67 and 69 open toprovide a third step ofunloading. Inasmuch as the valves 7 6'7- and 69 only operate after the first and sec- 0nd steps of unloading, the provision of unloader valves at one end only of the cyllnders does not impose an'undue unequal load upon the compressor.

Thefauxiliary control valve 44 operates from pressure passing the master control valve 21 through the passage49 and is set at a pressure higher than either of the auxiliary master control valves 42 or 43; When the auxiliary master control valve 44 is open,

pressure flows thereby through a conduit 71 to an unloader valve 72 in the rear end of the low pressure cylinder and through aconduit 73 to an unloader valve 74 provided in the rear end of the high pressure cylinder. These valves openin response to the pressure and provide a fourth step of unloading, whereupon the compressor'is" completely unloaded and discharges no pressure to the reservoir 18.

()bviously, by providing other auxiliary master'controlvalves, or by reducing the number-' of unloader valves opened at the first step of unloading and-providing other' auxiliary valves, the compressor may be unloaded in more than four steps, as I have'shown, and it is to be understoodthat I am not limited to the exact numberof steps shown.

The several valves utilized to accomplish the unloading steps just outlined will now be described. Referring toFig. 3, the master controlvalve 21 comprises avalve casing 81 having threads 82 on its lower end which: =;screwinto a threaded opening 83 provided in the housing 41. The casing 81*is held in shownindetail in Fig. 4. All ofthe auXilplace by a lock nut 84 having a beveled valve portion 86 fittingtightly against a compleduit 23 and which admits air'to the-interior of the casing, 81. Mounted Within the casingbottom of the opening 83 and held tightly v in place by the casing'81.

The plunger 88 is made hollow to accommodatea pin 96 which carries a spring abutment 97 at its upper end. A-spring 98 is mounted on the spring abutment 97 and an upper abutment 99 is screwed into a threaded opening 101 in the upper part of the casing 81. The upper abutment 99 serves as an adjusting spring'98. The adjusting nut 99' is provided with an opening 102 in its upper end and the lower spring abutment 97 has an upper portionextending through said opening so that the opening acts as a guide for the lower abutment. A cover'106 is'screwed downwardly over the upper endof the adjusting nut 99 and serves to lock it in adjusted position.

The casing 81' is open to the atmosphere through passages 104 provided above the; plunger 88 so that, should there be any leakage past said plunger it may pass freely to the atmosphere.

A particular feature of the master control valve is the formation of the valve portion 91 of the plunger 88, the valve portion being formed somewhat as an inverted cup. When the pressure beneath the plunger 88 exceeds the setting of the spring 98, the plunger 88 nut to regulate the tension of the is moved upwardly permitting air to pass the seat 93. The cup-like valve coacting with the seat 93 reversesthe direction of flow of the air so as toproduce a reactive effect upon the lunger 88 and move it to wide open position with the valve portion 89 seated against'the seat 92. Thus, the required volume of air is l iary master'control' valves are similar in construction and'a descrlption of one only will be given The'auXiliary master control valves are also similar in constrctuion to the master. control valve 21, the principal difference being the comparative sizes of. the valves. lhe'-auxilia'ry master control valve comprises-a double'seated plunger similie ' eaastructionand a detail description of only chambers 126 lar tp the plunger 88 already described and operable by pressure beneath the plunger supplied from the master control valve 21 throu h the passa e 46. The plunger 110 is against its lower seat by a spring 111 mounted and adjusted similar to the spring 98'inrthe master control valve 21. When the pressure beneath the plunger 110 exceeds the Seating of the spring 111 air passes by the lower seat of the plunger through the pasaagebl to rovide the operations already dema'ibed. When the plunger 110 is seated, after being opened, air trapped beyond the valve leaks past the plunger and passes to the atmos here through openings 112 provided in t e casing.

Referring now to Figs. 5 and 6, the auxili'arv valves 34 and 36 which control the first on second steps of unloading, will now be Both of the valves are similar in owfili be given. The valves-34 and 36 compti'accaeings 116 and 117 formed from a singlccasting and provided with shoulders 118 and 119 whichseat against recessed openand 122 provided in the housing 41 and extending-entirely through the housing. he "casings 116 and 117 are internally at their lower ends to receive plugs 123 and 124 each provided with a shoulder 125 hearing ainst the housing and which drew the casings tightly into engagement the housing 41 and prevent leakage thereby. The housing 41 is provided with and 127 in communication with the ges 47 and 51 to admit air for opwhen of the valves. The casing 116 is provided with an opening 128 and the casing .llfisrprovided with an opening 129 to adm1t,air to the interior thereof to effect their operation. Referring now particularly to Fig. 6, in the lower part of the casing 116 isa plunger 131 which fits substantially air 52 within said casing and normally rests on theiupper end of the plug 123. The plungerg 131 is made hollow to accommodate a the valve Aorgleaking past the plunger 131 passes to "M c .182which is also hollowed out to proair-abutment for a spring 133 interposed 132 and the plunger 131.

the Mmosphere through openings. 136 proividcd in the casing 116.

s tionl 1913 of. the casing 116 and provided with Thmvalve132 is provided with a beveled portion 137 which seats against a correspondingly shaped seat 138 in the casing116 when thdwalve is in its upper position; Mounted inthe upper part of the casing 116 is a hollow valve 141 havinga beveled portion 142 seata correspondingly shaped pora through the lower portion to balarms the pressure above and below it. The

valve 141 is provided with a stem 144 which extends into close proximity with a similar stem 146 provided on the valve 132. In the hollow of the valve 141 is provided a recess 147 for a spring 148 which biases the valve toward its seat and which is held in place by a cap nut 149 screwed into a threaded opening 151 in the casing 116. The cap 149 is bored out to form a guide for the valve and is provided, at its upper end, with a plug 150 which may be removed when necessary to grind the valve.

Relatively low pressure air from the reducing valve 28 enters the casing 116 through the conduit 33 above the valve seat 143 so that the valve 141 controls the flow of low pressure air to the conduit 52. The tension of the spring 148 is just sufficient to hold the valve 141 on its seat and prevent the passage of air thereby except when the valve is unseated'. When the master control valve- 21 opens, air flowing through the passages 47 acts on the plunger 131 forcing it and the valve 132 upwardly. The plunger 131 is provided with a beveled portion 153 which seats against a similarly formed seat 154 provided in the casing 116 when the plunger is in its uppermost position and prevents the leakage of air past the plunger. As the plunger moves upwardly it takes with it the valve 132 to its upper position where it seats against the seat 138, the spring 133 providing a cushion for the seating of the valve.

As the valve 132 moves upwardly, its stem 146 strikes the stem 144 of the valve 141, raising said valve off its seat and permitting the passage of low pressure air past said valve and outwardly t rough the conduit 52 to the unloader valve. When the master control valve 21 is again closed, the plunger 131 and valve 132 move to their lower position and air trapped in the conduit 52 passes to the atmosphere through the openings 136. At the same time, the valve 141 seats preventing the passage of low pressure air to the conduit While any well known form of unloader valve, which is operable in response to pressure to open the inlet valve its compression stroke, may be employed in my improved unloading system, I prefer to employ an unloader valve such as is illustrated in Fig. 7. Referring to this figure of the drawing, the cylinder wall is indicated at 161, a portion of the cooling space of the cylinder at 162, and the inlet passage into the cylinder at 163. The inlet valve comprises an upper valve seat 164 and a lower valveseat 166, the two being held together by a stud 167. Interposedbetween the seats 164 and 166 are a plurality of light metal rings 168 which constitute the opening and closing members of the inlet valve.

The seats 164 and 166 are located in a recess 169 in the cylinder wall and are held in position by a keeper 171. The keeper 171 is of a compressor and hold it open when the piston is making bored to form a shouldered recess 172 having which bear against the opening and closing members 168 of the inlet valve. The upper end 17 4 of the operating fork is free to slide in the bore 172 of the keeper 171.

The outer wall of the passage 163 is provided with an opening 177 over which fits a valve bonnet 178 which latter is provided with a threaded opening 179. An unloader valve casing 181 extends through the opening 179 and is provided, at its lower end, with a flanged portion 182 which bears against the bushing 173. The casing 181 is held in place by a surrounding nut 183 screwed into the opening 179 and having its lower end bearing tightly againstthe fiange182. The nut 183 is locked by a lock nut 180 screwed on the outer side thereofand having a beveled valve portion 185 fitting in a corresponding recess in the bonnet 178 and thus prevents outward leakage of air from the valve chamber. The flange 182 and the'casing 181 bear tightly against the upper end of the bushing 173 and the latter bearing against the keeper 171, holds the valve members 164 and 166 firmly in place in the recess 169.

Mounted within the valve casing'181' is a plunger 184 which is securechat its lower end, to the operating fork 174. The plunger 184 is made hollow and within the hollow thereof is a rod 186 which is slotted toward 3 its upper end to receive a pin 187 extending into the, wall of the casing 181 to prevent its being turned. The upper end of the stem 186 is provided with a cam portion'188 which coacts with a cam portion 189 of a valve oper ating stem 191, controlled by a handle 192 by means of which the plunger 184 may be manually forced downward, andthe rings 168 be forced off their upper seats'and the valve held open. a

The unloader valve is operated by the admission of air through an inlet opening 193 in the upper part of the casing 181 and which acts upon the plunger 184 to force it downwardly against the operating fork174, the action occuring upon the operation of the auxiliary valve associated with each partial unloader valve. The plunger 184 is pro vided, at its upper end, with a beveled valve portion 194 which bears, when the plunger is in its upper position, againsta correspondingly formed seat portion 196 formed in the valve casing 181 and thus prevents leakage of air past the plunger when the plunger is in its upper position, and when the pressure beneath the plunger is above atmospheric. Under such conditions, I may also employ a spring 197 to bear against the plunger 184 and which bears, at its upper end, against a ring abutment 198 secured to the rod 186.

The function of the spring 197 is to counterbalance the pressure in the intercooler and in the'inlet passage 163. Where the'unloader valve is employed in a-low pressure cylinder, having no pressure above atmospheric in the inlet passage, this spring may be dispensed with. i

' When no pressure is acting against the plunger 184 to move the operating fork 174 downwardly, it may be held in its upper po- I 'sition by a spring 185 disposed between the upper seat member 164 and the lower end of the plunger 184. In order to prevent knocking or hammering of the valve portion 194 of the plunger 184 when the valve mem- 1 bers .168 are closing due to velocity of air flowing therethrough, the fork 174 is'made a smooth sliding fit within the bore 172 so that an air cushion is formed between it and the bushing 173. The fork 174 being secured tolthe plunger 184, cushions the latter.

With the type of valve shown, the compressor piston, a fragment of'which is indicated at 201, in moving away from the valve,

causes the members 168 to open and admit air to the cylinder. Upon the compression stroke of the piston 201,-or in moving toward the 9 members 168, the velocity of the air being compressed carries the ring members upwardly against the upper seat7164 to close 1 7 them and prevent the escape of air back through the inlet 163. It will be seen that, if force be applied through the fork 17 4" to hold the members 168 off their seats, and this 9 force is insufficient to withstand the velocity of outflow of air past the members 168, they will be closed before the piston reaches the end of its stroke. v

This feature is taken advantage of by me to provide finer graduated steps of unloading'than has heretofore been possible. In accomplishing this purpose, I set the reducing 'valve 28 to provide a sufficiently low pressure to the auxiliary valves 34 and 36, which control the first and second steps of unloading, so that the velocity of air flowing past the members 168, during the compression stroke of the piston 201, overcomes the pressure acting against the-plunger 184 and forces the members 168 upwardly against their seats 164 toward the end of the stroke. By varying the setting of the reducing valve 28, I may thus vary the degree of unloading accomplished in the first and second steps.

From the foregoing description of my improved apparatus, as so far disclosed, the operation thereof will be readily understood. For example, assume that the compressor is to develop a maximum pressure of 102 poundsandit is to be unloaded in four steps such as has been illustrated. Undersuch conditions, the master control valve 211 may be set to open upon the attainment of 99 pounds pressure by the compressor. The auxiliary master control valve 42 is set to open at iso the auxiliary master control valve sat toopen at 101 ounds and the auxilcontrol va ve 44 is set to open Hi2 pounds. r olfwhcn he pressure within the reservoir 18 99 pounds, the master control valve 21 wide, as already explained, perl 11 air at 99 pounds pressure to pass to ill of tie auxiliary master control valves and w to the auxiliary valve 34. As soon as presssmre p to the auxiliary valve 34, it .torcoa the plunger 131 upwardly and opens thaywllve 141 to permit low pressure air to through the conduit 52 to the unloader M 53, 54, 56 and 57 on the low pressure ks'ylinder and to the unloader valves and 60 h pressure cylinder.

All of ass unloader valves being evenly Idividednbetween the opposed ends of the v the compressor is partially and Q9 mu unloaded so that no unequal strain is upon the driving motor. Further- .-mro, the pressure provided by the reducing value 28 is sufliciently low that the cylinder 3 m valves are forced against their seats velocity of air flowing thereby before I pistons complete their compression when the pressure within the reservoir 18 reaches 100 pounds, the master control valve 21;.being open, thejauxiliary master control "M842 is opened, operating the auxiliary .valvodidand opening the unloader valves 62 UM fiaintlao low pressure cylinder 10. This as PmY-ldes the second step of unloading and is W theme in operation as has already been defor the first step, the valves 62 and 63 closed by the velocity of air flowing I y. from the cylinder before the pis- Ao thn...-completes its compression stroke. The I new is now running at a greatly re timed load so that no undue strain is plaice? jthareupon b further unloading at one en 0 alchtof the cylinders.

l1 the pressure in the reservoir 18 when 101 pounds, the auxiliary master control palve 43 opens permitting high pressure thereby and flow to the unloader ralvesifil and 69, said valves being at the front ends of the low pressure cylinder 10 and thehigh pressure cylinder 11, respectively.

The pressure utilized for opening the valves {57 and 69,olosely approximating the maximum pressure to be developed, holds these valveswide open throughout the compression stroke of the piston. When the pressure the reservoir 19 has reached 102 poundg the auxiliary master control valve is opened to permit the pressure at which it imo to pass to the unloader valves 72 74 at the rear ends, respectively, of high pressure cylinders. When the compressor is completely unloaded and no ai r is being compressed, the valves and 74 also being held ofl their seats throughout the comprcssionstroke of the piston.

As the ressure within the reservoir 18 drops,-load is taken on in the reverse order just described. The auxiliary master control valve 44 first closes whereupon air trapped within the conduits 71 and 73 leaks to the atmosphere past the plunger 110 permitting the associated inlet valves to again operate. If the pressure continues to drop, the auxiliary master control valve 43 closes followed by the auxiliary master control valve 42 and finally, by the closing of the master control valve 21 whereupon the compressor is again under full load.

Referring now to Fig. 8 of the drawings, I show a modified form of my invention in which I employ a master control valve 210 and auxiliary master control valves 211, 212 and 213. These valves are constructed and operate in the same manner as that already described for the valves 21, 42, 43 and 44 and the detail description thereof need not be repeated. In this arrangement, however, I operate the auxiliary master control valves in series with each other. \Vhen the master control valve 210 opens, pressure passing thereby flows through a conduit 214 to the auxiliary master control valve 211, which latter is set to open at a higher pressure, and also flows through a branch conduit 216 to an auxiliary valve 217 similar to the valves 34 and 36 already described, to effect operation of an unloader valve or valves indicated diagrammatically at 218.

Upon a further rise of pressure, the auxiliary master control valve 211 opens, passing pressure through a conduit 219 to the auxiliary master control valve 212 and also supplying pressure through a branch conduit 221 to an unloader valve or valves 222. Upon a further rise in pressure, the auxiliary master control valve 212 opens, permitting pressure to flow through a conduit 223 to the auxiliary 'master control valve 213 and through a branch conduit 224 to an unloader valve or valves 226. With a still further rise in pressure the auxiliary master control'valve 213 is opened by pressure passing the previous valves, to effect operation of an unloader valve or valves 227.

With the arrangement shown in either modification of my invention, it will be apparent that I provide means for a gradual, even unloading of the compressor and that the unloading may be eflected in any desired number of steps.

It will furthermore be apparent that, having provided a single master control valve, which controls the operation of all the other valves, I have provided means whereby, should the unloader system get out of order for any reason, the trouble may be located more quickly than would be the case where a plurality of control valves are employed,

. sure for operating each responsive to the reservoir pressure. Thus, in locating trouble, the master control valve is first examined and if found in good operating condition, the succeeding valves are next examinedinthe order of their operation. V

From the foregoing it will be apparent that I have devised an improved unloader system for compressors which is sturdy of design, reliable in operation, and which may be adjusted to effect accurately and closely separated steps of unloading.

While I have shown my invention in but two forms, it will be obvious to those skilled in the art that it is not so limited but is susceptible of various other changes and modifications without departing from the spirit thereof and I desire therefore that only suclrlimitations shall be placed there upon as are imposed by the prior art or-as are specifically set forth in the appended claims. i

What I claim is:

1. In an unloader apparatus for a compressor, .the'combinationof a plurality of unloader valves adapted to be opened by pressure in opposition to the velocity of the medium being compressed flowing thereby when open, a master control valve responsive to the pressure developed by the compressor and adapted to be opened upon the attainment of a predetermined pressure by the compressor, and: a plurality of auxiliary valves operable in response to pressure passing the master control valve and adapted to supply difierentpredetermined pressures to operate the several unloader valves.

7 2. In an unloader apparatus for a compressor, the combination of a plurality of unloader valves adapted tobe opened by pressure in opposition to: the velocity of medium being compressed flowing thereby when open, a master control valve responsive .to the pressure developed by the compressor and adapted to'be opened upon the attainment of a predeterminedpressure, and an auxiliary valve operableupon opening of the master control valve and efiective to supply a predetermined relatively low presa first step unloader valve.

3. In an unloader apparatus for a compressor, the combination of a plurality of unloader valves adapted to be opened by pressure in opposition to the veloc1ty of medium being compressed flowing thereby when open, a master control valve responsive to the pressure developed by the com pressor and adapted to be opened upon'the attainment of a predetermined pressure, an'

auxiliary valve operable upon opening of the master control valve and efiective to supply a predetermined relatively low pressure for operating a first step unloader valve, an auxiliary master control valve operable upon an increase in pressure passing the trol valves master control valve, and a second auxiliary relatively low pressure to a second step unloader valve and operated by pressure passing the auxiliary master control'valve.

t. In an unloader apparatus for an air compressor, the combination 01. a spring biased master control valve operated by the pressure developed by the compressor, a plurality of spring biased auxiliary master control valvesin communication with the master control valve and operable at prov gressively increased pressures by the pressure passing the master control valve, and a plurality of pressure operated unloader valves in communication with the auxiliary master control valves and operated by pressure de- I livered by said latter valves.

5. In an unloader apparatus for an air compressor, the combination of a spring biased mastercontrol valve operated by the pressure developed by the compressor, a plurality of spring biased auxiliary master conin communication with the master control valve and operable at progressively increased pressures by the pressure passing the master control valve, a source of pressure lower thanthe pressure developed by the compressor; an auxiliary master control valve controlling the flow of lower pressure and operated by the pressure passing the master control valve, and an unloader valve in communication with the low pressure portion of the auxiliary valve and adapted to be opened by pressure acting in opposition to the velocity of air expelled through it by the action of the compressor when said valve is open. 1 r

6. In an unloader apparatus for an air compressor, the combination of a reservoir into which the compressor discharges, a master control valve operable upon the attainment out a )redetermined reservoir pressure, a pluality of unloader valves operable by air pressure, a plurality of auxiliary control valves governing the action of the unloader valves,

and actuated responsive to operation of the master control valve, a source or pressure lower than the reservoir pressure, and means automatically operable upon opening of the master control valve by an excess of reservoir pressure to subject some or n the unloader valves to the low pressure for opening said unloader valves.

In an unloader apparatus for a compress'or embodyin a cylinder and a reciprocating piston therein, the combination of a plurality of unloader valves communicating with the cylinde-rand adapted .to be opened by pressure in opposition to the velocity of the medium being compressed flowing thereby when open, and means for supplyinga predetermined relatively low pressure for opening some of said valves to provide a first step of unloading, said pressure being sufficientlylow for the unloader valves to be closed by veloeity f the medium being compressed before the piston reaches the end of its stroke.

- 8.. In an unloader apparatus for a compresour ying a cylinder and a reciprocating piston therein, the combination of a plurality ofunloader valves communicating with the cylinder and adapted to be opened by pressure in opposition to the velocity of the medium being compressed flowing thereby when open, and means for supplying a predetermined relativel low pressure for opening some-of said va ves to provide a first step of unloading, said pressure being sufliciently low for the unloader valves to be closed by velocity of the medium being compressed beiqtalthe piston reaches the end of its stroke and an equal number of said valves. being ar-. ianged at opposite ends of the cylinder. 29 fla -luau unloader apparatus for a compressob embodying a cylinder with a reciprocatingpiston therein, the combination of a plura it of unloader valves arranged with an equa .number at the opposite ends of the cylinders and operable by pressure in opposition to the velocity of the medium being compressed flowing thereby when open, and means responsive to the pressure developed by thecompressor for supplying a predeterao mmsdlow pressure to operate an opposed oitheunloader valves to provide a first xgpf unloading for the compressor. w Ill, In an unloader apparatus for a comprmorembodying. a cyllnder with a reciproas cat piston therein, the combination of a pl y of unloader valves arranged with an oil at the opposite ends of the cyla; and operable by pressure in opposition I velocity of the medium being com- PW flowing thereby when open, means resphilsive to the pressure developed by the compressor for supplying a predetermined loiapressure to operate an opposed pair of the unloader valves to provide a first step of unloading for the compressor, and means responsive to a pressure developed by the commssor above that required to effect operaion of the first step of unloading for supplyair at a redetermined low pressure to operate anot er opposed pair of unloader valves to provide a second step of unloading for the compressor, the low pressure supplied to both the first and the second step unloader valves being suflicientlv low for said unloader valves to be closed by velocity of the medium compressed flowing thereby before the piston completes its stroke.

an unloader apparatus for a compressor embodying a cylinder with a reciproa'at' piston therein,'the combination of a plu r b lit of unloader valves arranged with an equ number at the opposite ends of the c finders and operable by pressure in oppo sition-to the velocity of the medium being compressed flowing thereby when open,

means responsive to the pressure developed by the compressor for supplying a predetermined low pressure to operate an opposed pair of the unloader valves to provide a first step of unloading for the compressor, means responsive to pressure developed b the compressor above that required to eflect operation of the first step of unloading for supplying air at a predetermined low pressure to operate another opposed pair of unloaded valves to provide a second step of unloadin for the compressor, the low pressure supplie to both the first and second step unloader valves being sufliciently low for said unloader valves to be closed by velocity of the medium compressed flowing thereby before the piston completes its com ression stroke, and means responsive to a stillhigher pressure developed by the compressor for supplying pressure for operating the remaining unloader valves. 7 12. In an unloader apparatus for a compressor, the combination of a plurality of unloader valves operable responsive to pressure, a plurality of auxiliary valves controlling the operation of the unloader valves, and a master control valve responsive to the pressure developed by the compressor for controL ling the operation of the auxiliary valves.

13. In an unloader apparatus for a compressor, the combination of a plurality of unloader valves operable responsive to pres sure, a plurality of auxiliary valves controlling the operation of the unloader valves, and a master control valve responsive to the pressure developed by the compressor for controlling the operation of the auxiliary valves, said auxiliary valves operating in series with the master control valve and with each other.

14-111 an unloader apparatus for a compressor, the combination of a plurality of unloader valves operable responsive to pressure, a master control valve responsive to the pressure developed by the compressor, and a plurality of auxiliary valves operating in series with the master control valve and controlled thereby, said auxiliary valves controlling the operation of the unloader valves.

15. In an unloader apparatus for a compressor, the combination of a plurality of unloader valves operable responsive to pressure, a master control valve responsive to pressure develgped by the compressor and permitting the ow of pressure thereby when open, and a plurality of auxiliary valves controlling the operation of the unloader valves and operated by pressure flowing past the master control valve.

16. In an unloader apparatus for a compressor, the combination of a plurality of unloader valves operable responsively to pres sure, a master control valve, a spring biased plunger embodied in the master control valve and subject to the pressure developed by the compressor, a cup shaped beveled valve portion formed on the plunger, a cone shaped seat coacting with the valve portion to provide a reactive eflect on the plunger when the pressure overcomes the plunger spring and to'open the valve Wide permitting a flow of pressure thereby, and a plurality of auxiliary valves controlling the operation of the unloader valves and operated by pressure flowing past the master control valve.

17. In an unloader apparatus for a compressor, the combination of a plurality of unloader valves operable responsively to pressure, a master control valve, a spring biased plunger embodied in the master control valve and subject to the pressure developed by the compressor, a cup shaped beveled valve portion formed on the plunger, a cone shaped seat coacting with the valve portion to provide a reversal of direction of air flow past the seat and to produce a reactive efiect on the plunger when the pressure overcomes the plunger spring to open the valve wide permitting a flow of pressure thereby, and a plurality of auxiliary valves controlling the operation of the unloader valves and operated by pressure flowing past the master control valve, said auxiliary valves being arranged to operate in series with each other.

18. In an unloader apparatus for a compressor, the combination of a. plurality of un loader valves operable responsively to pressure, a master control valve, a spring biased plunger embodied in the master control valve and subject to the pressure developed by the compressor, a cup shaped beveled valve portion formed on the plunger, a cone shaped seat coacting with the valve portion to provide a reversal of air flow and a reactive effeet on the plunger when the pressure overcomes the plunger spring to open thevalve wide permitting a flow of pressure thereby, a valve casing supplied by pressure from the master control valve, a plunger in the casing subjected to the pressure from the master control valve, a source of relatively low pressure communicating with the valve casing, a discharge conduit for the relatively low pres sure and connected to the valve casing, a

' valve within the casing for controlling the discharge of low pressure air and operated by the plunger, and an unloader valve in communication with the discharge conduit and operable by the pressure in said discharge conduit.

19. In an'unloader apparatus for a compressor, the combination of a plurality of un loader valves operable responsively to pressure, a master control valve, a spring biased plunger embodied in the master control valve and subject to the pressure developed by the compressor, a cup shaped beveled valve portion formed on the plunger, a cone shaped seat coacting with the valve portion to provide a reversal of air flow and a reactive effeet on the plunger when the pressure overcomes the plunger spring to open the valve wide permitting a flow of pressure thereby, a valve casing supplied by pressure from the master control valve, a plunger in the casing subjected to the pressure from the master control valve, a source of relatively low pressure communicating with the valve casing, a discharge conduit for the relatively low pressure and connected to the valve casing, a valve within the casing for controlling the discharge of low pressure air and operated by the plunger, spring means interposed between the plunger and the valve to cushion the movements of the latter, and an unloader valve in communication with the discharge conduit and operable by the pressure in said discharge conduit,

In testimony whereof I affix my signature.

WILLIAM E. MATHEWS. 

